Spontaneous Epileptiform Discharges in Hippocampal Slices Induced by 4-aminopyridine

Brain Res. 1985 Sep 2;342(1):54-66. doi: 10.1016/0006-8993(85)91352-6.

Abstract

4-Aminopyridine (4-AP) induced 2 types of spontaneous field potentials (SFPs) in the hippocampal slice. Type I resembled spontaneous activity induced by other convulsants. They occurred at a rate of approximately 1 Hz, started in the CA2/CA3 region and spread at a velocity of 0.3 m/s to area CA1. Transsection experiments and laminar profiles indicated that they spread synaptically along the Schaffer collateral pathway. Synaptic blockade by low Ca2+/high Mg2+ or kynurenic acid reversibly abolished type I SFPs. Increasing [Ca2+]o lowered the rate and slightly increased the amplitude. Possibly, increased spontaneous transmitter release, and not disinhibition, is responsible for the generation of type I SFPs. Type II occurred at a rate of about 0.15 Hz and travelled in the same direction, but a factor 10 slower. They could not be blocked by separation of the CA1 and CA3 region; coupling remained until stratum moleculare was severed. Type II could not be suppressed by blockade of synaptic transmission. The laminar profile is similar in shape to that of type I but not identical. Increasing [Ca2+]o had the same but stronger effect as on type I. Type II SFPs depressed evoked population spikes up to a second and delayed the next type I SFP. The mechanisms involved remain largely speculative; further analysis is needed to help understand the epileptogenic action of 4-AP.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 4-Aminopyridine
  • Aminopyridines / pharmacology*
  • Animals
  • Female
  • Hippocampus / drug effects*
  • Hippocampus / physiology
  • In Vitro Techniques
  • Male
  • Membrane Potentials / drug effects
  • Rats
  • Rats, Inbred Strains
  • Seizures / chemically induced*
  • Seizures / physiopathology

Substances

  • Aminopyridines
  • 4-Aminopyridine